1. Field of the Invention
The present invention relates to an idling speed control system for an engine of an automotive vehicle, and more particularly to an idling speed control system for controlling an idling speed of the engine in accordance with operation of a refrigeration circuit of an air conditioner or the like for the vehicle.
2. Description of Prior Art
When an engine is maintained in idling operation in such prior art as disclosed in the laid-open Japanese patent publication No. 41951/1987, a quantity of an air-fuel mixture sucked into the engine in operative condition of a refrigeration circuit is controlled to increase compared with the air-fuel mixture quantity in inoperativeness of the refrigeration circuit, taking account of pressure in a high-pressure circuit portion of the refrigeration circuit. This prevents rough idling or stalling of the engine, even if load acting on the refrigeration circuit increases.
When a variable capacity type compressor is adopted as a compressor of the refrigeration circuit, large driving torque is required for driving the compressor, because of an increase in capacity of the compressor as decrease of a rotational speed of the compressor if a quantity of refrigerant circulated through the refrigeration circuit is maintained in constant. When release of an accelerator pedal for the vehicle changes an operative state of the engine from a normal running state to an idling state, the actual rotational speed of the engine is lowered suddenly down to a predetermined idling speed, whereas the actual capacity of the compressor is changed rapidly from a small capacity to a large capacity in such a manner to maintain a required quantity of the refrigerant to be circulated. Thus, a quantity of the refrigerant to be circulated immediately after change of the engine to the idling operation is maintained in a value required immediately before change of the engine to the idling operation without sudden changes of refrigerant quantity. Furthermore, a load acting on the engine is suddenly increased due to a sudden increase of the driving torque for the compressor, at the time when an operative state of the engine changes from the normal running state to the idling state.
If an increase of an air-fuel mixture during the idling operation of the engine is not so set large, a quantity of an air-fuel mixture supplied to the engine becomes short to thereby cause rough or stalling operation of the engine upon change of the engine to the idling operation, when cooling ability of the refrigeration circuit before change of the to the idling operation is maintained high to maintain the compressor driving torque and refrigerant flow quantity increased. If an increase of an air-fuel mixture during the idling operation of the engine is inversely set large, a quantity of the air-fuel mixture supplied to the engine in its idling operation is excessively increased to cause bad fuel consumption when cooling ability of the refrigeration circuit before change of the engine to the idling operation is not so maintained high or a quantity of the refrigerant to be circulated is not so maintained much.